1. Field of the Invention
This invention relates to laser equipment which can both scan a laser beam and adjust the optical path to achieve a variable focal length of the laser beam.
2. Description of Prior Art
Laser scanning systems typically utilize galvanometer motors to change the angle of scanning mirrors. Usually the X and Y direction is scanned by separate motors. In many applications a laser beam is scanned on a work piece. To achieve a high power density, the laser beam is usually focused on this work piece. Specialized lens have been developed to achieve a good focus on a flat surface work piece even at a high transmission angle. However, some applications require that the laser beam can be independently focused to accommodate a contoured surface. Normally this focusing is accomplished by translating one or more lenses in an optical system to achieve a variable focal length. Unfortunately, high powered CO.sub.2 lasers can cause a thermal distortion in lenses which degrades the quality of the laser beam. Furthermore, lenses are not as durable as metal mirrors for high power laser beam applications. Therefore, it is desirable to utilize all reflective optic components for high power CO.sub.2 laser applications. Here a problem arises when making a scanning system with a variable focal length. A change in the focal length requires a change in the optical path length. With reflective optics, a path length change usually also produces an undesirable steering of the beam. The invention presented here is an all reflective laser scanning system where a focus adjustment can be made with a minimum of translationable motion and also without introducing any steering or translation of the laser beam.